Pre-disposing factors• Age• Virulent organisms• Cholesteatoma or Bone erosion• Presence of a congenital dehiscence• Obstruction of drainage e.g polyp• Low resistance of the patient• Poor socio-economic status
Routes of spread
Pathways of infections• The commonest way for extension of infection is by bone erosion due to a cholesteatoma.• Vascular extension (retrograde thrombophlebitis). • Extension along preformed pathways as– Congenital dehiscences, fracture lines, round window membrane, the labyrinth,– Dehiscences due to previous surgery.
Lateral Sinus Thrombosis (sigmoid sinus)Spread of infection by direct extension orvia mastoid emissary vein ↓ Pus and granulation adjacent to sigmoidsinus ↓ Reactive thrombophlebitis ↓ intraluminal thrombus ↓ CSF obstruction